Youngest your child understood pregnancy/baby in belly

I am 13 weeks with baby number 3. My oldest will be 4 in April 😭 I got pregnant with his sister when he was 19 months old and throughout pregnancy I would say baby and he would come rub my belly and kiss it. Once we knew gender you’d ask where is sissy/Lyla and he would come to my belly. When she was born, I told him this is Lyla and he got a huge o face on his face, it was adorable. I am now pregnant with number 3. We found out when Lyla was 15 months. She’s now almost 18 months and when I say baby she runs up to me and touches my belly and when she is nursing she rubs it. Wondering if she’ll understand more throughout also. I am due August 3. I was due for her August 10. Her birthday is August 7 so she will most likely be a big sister before she turns 2

Just curious how young your kids understood you were pregnant.